Optimize away a blst_fr_eucl_inverse call

ethereum · Sep 16, 2024 · 1c67090 · 1c67090
1 parent 2c03989
commit 1c67090
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Showing 2 changed files with 2 additions and 4 deletions.
diff --git a/src/eip4844/eip4844.c b/src/eip4844/eip4844.c
@@ -81,7 +81,6 @@ static bool fr_is_zero(const fr_t *p) {
  * @param[in]   a   A vector of field elements, length `len`
  * @param[in]   len The number of field elements
  *
- * @remark This function only supports len > 0.
  * @remark This function does NOT support in-place computation.
  * @remark Return C_KZG_BADARGS if a zero is found in the input. In this case,
  *         the `out` output array has already been mutated.

diff --git a/src/eip7594/eip7594.c b/src/eip7594/eip7594.c
@@ -648,9 +648,8 @@ static C_KZG_RET compute_commitment_to_aggregated_interpolation_poly(
 
         /* Now divide by the coset shift factor */
         uint64_t pos = reverse_bits_limited(CELLS_PER_EXT_BLOB, i);
-        fr_t inv_coset_factor;
-        blst_fr_eucl_inverse(&inv_coset_factor, &s->roots_of_unity[pos]);
-        shift_poly(column_interpolation_poly, FIELD_ELEMENTS_PER_CELL, &inv_coset_factor);
+        uint64_t idx = FIELD_ELEMENTS_PER_EXT_BLOB - pos % FIELD_ELEMENTS_PER_EXT_BLOB;
+        shift_poly(column_interpolation_poly, FIELD_ELEMENTS_PER_CELL, &s->roots_of_unity[idx]);
 
         /* Update the aggregated poly */
         for (size_t k = 0; k < FIELD_ELEMENTS_PER_CELL; k++) {